This error occurs when using basic authentication (username/password) for your NetSuite connection. Token-based authentication (TBA) is more secure, and you should update to TBA for NetSuite connections since NetSuite 2018.2 and above requires two-factor authentication (2FA) for any Administrator, Full Access, or other highly privileged role.
For steps on switching your NetSuite connection from basic authentication to token-based authentication, see Change NetSuite connection to two-factor authentication (2FA) for 2018.2.